The Internet, and particularly the world-wide-web, is a rapidly growing network of interconnected computers from which users can access a wide variety of information. Initial widespread use of the Internet was limited to the delivery of static information. A newly developing area of functionality is the delivery and execution of complex software applications via the Internet. There are two basic techniques for software delivery, remote execution and local delivery, e.g., by downloading.
In a remote execution embodiment, a user accesses software which is loaded and executed on a remote server under the control of the user. One simple example is the use of Internet-accessible CGI programs which are executed by Internet servers based on data entered by a client. A more complex system is the Win-to-Net system provided by Menta Software. This system delivers client software to the user which is used to create a Microsoft Windows style application window on the client machine. The client software interacts with an application program executing on the server and displays a window which corresponds to one which would be shown if the application were installed locally. The client software is further configured to direct certain I/O operations, such as printing a file, to the client's system to replicate the “feel” of a locally running application. Other remote-access systems, such as one provided by Citrix Systems, are accessed through a conventional Internet Browser and present the user with a “remote desktop” generated by a host computer which is used to execute the software.
Because the applications are already installed on the server system, remote execution permits the user to access the programs without transferring a large amount of data. However, this type of implementation requires the supported software to be installed on the server. Thus, the server must utilize an operating system which is suitable for the hosted software. In addition, the server must support separately executing program threads for each user of the hosted software. For complex software packages, the necessary resources can be significant, limiting both the number of concurrent users of the software and the number of separate applications which can be provided.
In a local delivery embodiment, the desired application is packaged and downloaded to the user's computer. Preferably, the applications are delivered and installed as appropriate using automated processes. After installation, the application is executed. Various techniques have been employed to improve the delivery of software, particularly in the automated selection of the proper software components to install and initiation of automatic software downloads. In one technique, an application program is broken into parts at natural division points, such as individual data and library files, class definitions, etc., and each component is specially tagged by the program developer to identify the various program components, specify which components are dependent upon each other, and define the various component sets which are needed for different versions of the application.
Once such tagging format is defined in the Open Software Description (“OSD”) specification, jointly submitted to the World Wide Web Consortium by Marimba Incorporated and Microsoft Corporation on Aug. 13, 1999. Defined OSD information can be used by various “push” applications or other software distribution environments, such as Marimba's Castanet product, to automatically trigger downloads of software and ensure that only the needed software components are downloaded in accordance with data describing which software elements a particular version of an application depends on.
Although on-demand local delivery and execution of software using OSD/push techniques is feasible for small programs, such as simple Java applets, for large applications, the download time can be prohibitively long. Thus, while suitable for software maintenance, this delivery system is impractical for providing local application services on-demand because of the potentially long time between when the download begins and the software begins local execution.
Recently, attempts have been made to use streaming technology to deliver software to permit an application to begin executing before it has been completely downloaded. Streaming technology was initially developed to deliver audio and video information in a manner which allowed the information to be output without waiting for the complete data file to download. For example, a full-motion video can be sent from a server to a client as a linear stream of frames instead of a complete video file. As each frame arrives at the client, it can be displayed to create a real-time full-motion video display. However, unlike the linear sequences of data presented in audio and video, the components of a software application may be executed in sequences which vary according to user input and other factors.
To address this issue, as well as other deficiencies in prior data streaming and local software delivery systems, an improved technique of delivering applications to a client for local execution has been developed. This technique is described in parent U.S. patent application Ser. No. 09/120,575, now U.S. Pat. No. 6,311,221, entitled “Streaming Modules” and filed on Jul. 22, 1998. In a particular embodiment of the “Streaming Modules” system, a computer application is divided into a set of modules, such as the various Java classes and data sets which comprise a Java applet. Once an initial module or modules are delivered to the user, the application begins to execute while additional modules are streamed in the background. The modules are streamed to the user in an order which is selected to deliver the modules before they are required by the locally executing software. The sequence of streaming can be varied in response to the manner in which the user operates the application to ensure that needed modules are delivered prior to use as often as possible.
Although an improvement over existing streaming technology, the “Streaming Modules” methodology generally operates on software-program boundaries and therefore the streaming is flexibility is constrained to some extent by the structure of the application files and the application itself. In addition, in one embodiment, client-side streaming functionality is added to the streamed program through the use of stub routines inserted into the program code. Thus, the source or object code of the program must be modified to prepare them for streaming.
In a newly developed application streaming methodology, described in copending U.S. Patent Application entitled “Method and System for Executing Network Streamed Applications”, filed concurrently with the present application, the client system is provided with client-side streaming support software which establishes a virtual file system (“VFS”) and connects it to the client's operating system such that the virtual file system appears to be a storage device. The VFS is configured as a sparsely populated file system which appears to the operating system to contain the entire set of application files but, in practice, will typically contain only portions of selected files. Client streaming functionality is provided to process streamlets or blocks of individual files and add them to the VFS as appropriate.